1. Field of the Invention
The present invention relates to a suck back valve capable of avoiding any liquid drip, for example, from a supply port for a pressure fluid by sucking a predetermined amount of the pressure fluid flowing through a fluid passage.
2. Description of the Related Art
A suck back valve has been hitherto used, for example, in steps for producing semiconductor wafers or the like. The suck back valve has a function to avoid the so-called liquid drip in which a minute amount of coating liquid is dripped from a supply port to the semiconductor wafer when the supply of the coating liquid to the semiconductor wafer is stopped.
Such a conventional suck back valve is now shown in FIG. 5 (see, for example, Japanese Patent Publication No. 6-47092).
The suck back valve 1 includes a main body 5 which is formed with a flow chamber 4 for making communication between an inflow port 2 and an outflow port 3, and a cover 6 which is connected to an upper portion of the main body 5. The inflow port 2 is connected to a discharge liquid supply source 19 via an ON/OFF valve 18 which is constructed separately from the suck back valve 1. On the other hand, the outflow port 3 is connected to a nozzle 19a which drips the coating liquid toward the semiconductor wafer.
An opening 7, which extends upwardly, is formed at a substantially central portion of the flow chamber 4. A first diaphragm 8, which closes the upper surface of the flow chamber 4 in an air-tight manner, is stretched over the opening 7. A vertically movable member 10, which abuts against the first diaphragm 8 at the lower end, is arranged in an accommodation chamber 9 which is formed over the first diaphragm 8.
A second diaphragm 11, which is interposed between the main body 5 and the cover 6, is arranged at an upper portion of the vertically movable member 10. The second diaphragm 11 moves together with the vertically movable member 10 by the aid of a projection 12 which is caulked to the end of the vertically movable member 10 and which is secured to the second diaphragm 11.
A coil spring 13, which urges the second diaphragm 11 upwardly, is installed between the first diaphragm 8 and the second diaphragm 11. A pressure chamber 15, to which the pilot air is supplied via a pilot air port 14, is formed between the second diaphragm 11 and the cover 6. A detecting unit 17, which is provided with a detecting pin 16 to make abutment against the projection 12 of the vertically movable member 10, is provided on the cover 6.
The operation of the conventional suck back valve 1 will be briefly explained. When the ON/OFF valve 18, which is constructed separately, is in the ON state, and the liquid is supplied from the discharge liquid supply source 19, then the pressure chamber 15, to which the supply is effected from an unillustrated electropneumatic proportional valve to the pilot air port 14, has a high pressure. The second diaphragm 11 is located at the lower position indicated by the two-dot chain line shown in FIG. 5 while elastically compressing the coil spring 13. The first diaphragm 8, which is operated integrally with the vertically movable member 10, is also located at the lower position, and the volume of the flow chamber 4 is small.
Starting from the state as described above, when the ON/OFF valve 18 is switched to the OFF state to stop the supply of the liquid, then the pilot pressure, which is supplied from the pilot air port 14, is reduced, and the pressure in the pressure chamber 15 is lowered. Therefore, the first diaphragm 8 is moved upwardly together with the second diaphragm 11 and the vertically movable member 10 to give a state indicated by the solid line in FIG. 5. As a result, the first diaphragm 8 is deformed, and the volume of the flow chamber 4 is increased. Accordingly, the liquid remaining in the nozzle 19a is sucked.
However, in the case of the conventional suck back valve 1 as described above, the ON/OFF valve 18, which is constructed separately from the suck back valve 1, is used to allow the liquid to flow along the flow chamber 4 and/or stop the flow of the liquid. For this reason, the installation space is increased, and it is required to perform the piping operation for connecting the ON/OFF valve 18 and the suck back valve 1, which is complicated.